Field of invention

The present invention relates to continuous process for the preparation of 6-APA i.e. 6-Aminopenicillanic acid of formula (I) with recovery of PAA i.e. Phenyl acetic acid.

Background of the invention

6-APA is chemically known as 6-Aminopenicillanic acid, having molecular formula C8H12N2O3S and molecular weight 216.26. It is well-known that 6-APA i.e. 6-Aminopenicillanic acid may be produced by the action on a penicillin of certain enzymes which split the amido bond of the penicillin. The enzymes which are known to split this amido bond are hereinafter termed penicillin deacylase enzymes, though they may also be described as penicillin amidase.

6-Aminopenicillanic acid, commonly referred to as 6-APA, is an intermediate in the manufacture of synthetic penicillins and is prepared among other means by the deacylation of penicillins. This conversion has been effected by both chemical and biochemical techniques. The chemical conversion, as exemplified by U.S. Pat. No. 3,499,909 suffers from being a multi-step process requiring energy-intensive low-temperature conditions and specialized equipment. The biochemical conversion utilizes the enzyme penicillin acylase, or penicillin amidase. In U.S. Pat. No. 3,260,653, the enzyme activity is supplied by certain bacteria or bacterial extracts. This approach is not entirely satisfactory for the industrial production of 6-APA since the product stream is contaminated with the enzyme and/or microbial cells, which must then be removed during product recovery, and the enzyme is used only once. The problems of product contamination and poor enzyme utilization are purportedly overcome in U.S. Pat. No. 3,953,291 by the use of immobilized penicillin amidase-producing microbial cells. Such a process using immobilized cells is still characterized by low productivity, however, since in batch operation the process suffers from its non-continuous nature and excessive handling of the immobilized cell material, while in column operation it suffers from poor pH control and less than optimum enzyme utilization. The use of a shallow bed of microbial cell catalyst for the continuous isomerization of glucose to fructose is disclosed in U.S. Pat. Nos. 3,694,314 and 3,817,832. The shallow bed is reportedly employed to minimize the pressure drop through the catalyst, the desired conversion being achieved by passing the aqueous process stream through several beds in series.

There is a need to develop which devoid the drawbacks that adhered with prior processes. Therefore to overcome these drawbacks present inventors develop a continuous process which not only gives consistent high yield and purity of 6-APA but also recovers phenyl acetic acid efficiently.

Objects of the invention

The primary object of present invention is to provide a continuous process for the preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid.

Another object of present invention is to provide a continuous process for the preparation of 6-amino penicillanic acid.

Another object of present invention is to provide a continuous process for the preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid comprising steps of:
a) enzymatic hydrolysis of Penicillin-G salt to 6-APA in continuous stirred tank reactor
b) passing a solution obtained in step (a) through plug flow reactor
c) extracting aqueous solution of 6-APA obtained in step (b) with dichloromethane by spiral extraction column
d) separating extracted mass obtained in step (c) in continuous gravity separator to obtain aqueous layer and organic layer
e) precipitating 6-APA crystals from aqueous layer obtained in step (d) in continuous precipitator and extracting organic layer of step (d) with aqueous ammonia for recovery of PAA
f) filtering 6-APA crystals obtained in step (e) by continuous filter and
g) drying 6-APA crystals obtained in step (f)

Another object of present invention is to provide a continuous process for the preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid comprising steps as described in fig. 1.

Another object of the present invention is to provide a continuous process for the preparation of 6-APA in high yield and purity with efficient recovery of PPA.

Yet another object of the present invention is to provide a continuous process for the preparation of 6-APA with the recovery of PPA, which is simple and easy to handle at production level.

Yet another object of the present invention is to provide a continuous process for the preparation of 6-APA with the recovery of PPA, which is extremely cost effective.

Yet another object of the present invention is to provide a continuous process for the preparation of 6-APA with the recovery of PPA, which provides consistent result with regards to yield and purity.

Summary of the invention

According to one aspect of present invention, it provides a continuous process for the preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid.

According to another aspect of present invention, it provides a continuous process for the preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid.

According to another aspect of the present invention provides a continuous process for the preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid comprising steps as described in fig. 1.

According to another aspect of the present invention, it provides a continuous process for preparation of 6-amino penicillanic acid with the recovery of phenyl acetic acid comprising steps of:
a) enzymatic hydrolysis of Penicillin-G salt to 6-APA in continuous stirred tank reactor
b) passing a solution obtained in step (a) through plug flow reactor
c) extracting aqueous solution of 6-APA obtained in step (b) with dichloromethane by spiral extraction column
d) separating extracted mass obtained in step (c) in continuous gravity separator to obtain aqueous layer and organic dichloromethane layer
e) precipitating 6-APA crystals from aqueous layer obtained in step (d) in continuous precipitator and extracting dichloromethane organic layer of step (d) with aqueous ammonia for recovery of PAA
f) filtering 6-APA crystals obtained in step (e) by continuous filter and
g) drying 6-APA crystals obtained in step (f)

According to another aspect of the present invention, it provides a continuous process for the preparation of 6-APA in high yield and purity with efficient recovery of PPA.

According to another aspect of the present invention, it provides a continuous process for the preparation of 6-APA with recovery of PPA, which is simple and easy to handle at production level.

According to another aspect of the present invention, it provides a continuous process for the preparation of 6-APA with recovery of PPA, which is extremely cost effective.

According to another aspect of the present invention, it provides a continuous process for the preparation of 6-APA with the recovery of PPA, which provides consistent result with regards to yield and purity.

Brief description of the accompanying figures

Fig. 1 depicts the flow diagram of a continuous process for preparation of 6-APA with recovery of PPA as accordance with the present invention.

Detailed description of the invention

In an embodiment, step (e) as defined hereinabove which involves extracting dichloromethane organic layer of step (d) with aqueous ammonia for recovery of PAA comprising steps of :
(i) extracting dichloromethane organic layer of step (d) with aqueous ammonia to obtain aqueous layer and dichloromethane organic layer
(ii) precipitating PAA from aqueous layer obtained in step (i) in continuous precipitator and recovering dichloromethane organic layer of step (i)
(iii) filtering and drying PPA obtained in step (ii)

In another embodiment, this invention provides hydrolysis of Penicillin-G to 6-APA at 28-35°C in presence of enzymes. The Principal process operation steps of continues manufacturing process of 6-APA are given as follows:-
A) Enzymatic Hydrolysis of Penicillin – G Potash salt to 6-APA
B) Extraction of Phenyl Acetic Acid from 6-APA aqueous reaction mass by using solvent Dichloromethane
C) Precipitation of 6-APA crystals
D) Filtration and Drying of 6 – APA crystals
E) Recovery of Phenyl Acetic Acid from Dichloromethane as byproduct.

For the purpose of this specification, the meaning of the term “6-APA” as used hereinabove is 6-Aminopenicillanic acid.

For the purpose of this specification, the meaning of the term “PAA” as used hereinabove is Phenyl acetic acid.

Continuous Stirred Tank Reactor (CSTR) (1) as used in step a) has following detailed information:-

This enzymatic reactor has 2000 ml working capacity which is made up of glass cylindrical shell with a 400 mesh size SS screen is placed at the bottom of CSTR to hold fine enzyme catalyst in vessel. The equipment is facilitated with a central SS shaft with two nos. of SS impellers (45 ° Down-flow Pitch blade Turbine) located apart to keep enzymes in uniform suspension. Agitation system is provided with a mechanical seal and an induction motor having ¼ HP power rating and 1440 rpm. A digital RPM controller (Make: Delta) can facilitate the alteration of agitation level potentiometrically. A facility of top insertion of pH electrode can measure the pH (7.8–8.2) of enzymatic reaction with a pH controller (Make: Prominent, Model: PHD Dulcometer). An aqueous stream of 8 % w/w concentration of Penicillin G-Potash salt is introduced at the rate of 40 ml/min at the top of reactor by using a Peristaltic Pump ( Make : ELECTROLAB , Model : PP-201 V).On other hand overflow pipe protected with SS screen on the CSTR can continuously drain aqueous mass of reaction product. Reaction acidity due to generation of Phenyl Acetic acid is neutralized continually by dosing of 4 % w/w aqueous ammonia solution.

Plug Flow Reactor – (PFR) (2) as used in step b) has following detailed information:-

This reactor is used for further conversion of penicillin G to 6-APA and removal of unconverted trace Penicillin G present in the reaction mass. PFR is a packed bed reactor filled with enzyme catalyst and supported by 400 mesh SS screen on both end. It is having 40 mm internal diameter and 250 mm packed bed height. Reaction mass from CSTR is further fed to PFR at rate of 80 ml/min by using a Peristaltic Pump (Make: ELECTROLAB, Model: PP-201 V). Product streams are withdrawn from PFR at a rate of 40 ml/min, while a recycle stream is returned back to PFR. Stream recycling maintains effective pH & Temperature control in re-circulation loop.

Spiral extraction column (3) as used in step c) has following detailed information:-

Extraction of Phenyl Acetic Acid was carried out in this spiral extraction column which is a spiral column having 50 mm diameter with 12 mm internal spiral coil. A jet mixer is provided on top of column to mix aqueous phase of reaction mass (PAA laden) and Dichloromethane. Special jet mixing design and vigorous baffles in mixing chamber, enables fast extraction of PAA into Dichloromethane in shorter residence time. Reaction mass is acidified with 33 % w/w HCl externally and pump into jet mixer on the top of extraction column at a rate of 40 ml/min. On other end Dichloromethane is pumped into jet mixer at a rate of 10 ml/min. Peristaltic Pump (Make: ELECTROLAB, Model: PP-201 V) is used to maintain desired flow conditions with sufficient feeding pressure. Chilled water is circulated in periphery of extraction column to maintain low temperature (0-5 °C) of extraction.

Continuous gravity separator as used in step d) has following detailed information:-

Extracted mass is settled in this separator which has 2000 ml capacity. Biphasic stream is fed in the centre of separator, and heavy phase dichloromethane layer is drained from the bottom part and aqueous reaction mass (PAA free) is over flowed out from the top of separator. A specific interphase level at the centre of separator is maintained which enables continuous separation of biphasic system.

Continuous precipitator (4) as used in step e) has following detailed information: -

This precipitator has a capacity of 4000ml. Aqueous reaction mass is continuously fed at a rate of 40 ml/min to a said precipitator which is equipped with a ribbon blender supported on a central shaft with motor, which enables precipitated crystals to move forward. A jacketed shell maintains 0-5° C temperature by chilled water. A pH electrode is top inserted in the centre of precipitator which can measure the pH (3.8– 4.2) of precipitated mass and is controlled with a pH controller (Make: Prominent, Model: PHD Dulcometer) by using 20 % w/w aqueous ammonia solution charged uniformly over the length of precipitator. A sonotrode placed at the feed location can improve the rate of nucleation. Precipitated 6-APA slurry is continuously drain out at a rate of 40 ml/min from opposite end of precipitator.

Continuous filter (5) as used in step f) has following detailed information: -

Precipitated 6-APA crystals are isolated continuously by using this filter. Continuous filter is a perforated conical screen as shown in figure wrapped with a fine filter screen (400 mesh). A conveyor screw is placed in conical part of screen supported on a central shaft with motor. Under vacuum filtration enables 6-APA crystal filtration at a rate of 40 ml/min.

Filtered wet crystals is vacuum dried in a vacuum dryer (6) at 45-50 °C for 6-8 hrs , while maintaining required moisture content.

Detailed information of Spiral extraction column (7), Continuous precipitator (8) and Continuous filter (9) used in recovery process of PAA is same as defined above.

Advantages of the present inventions:-

1. Lower utility cost per kg of 6-APA manufactured compare to batch process :
In a continuous unit operation or processes once the steady state is achieved, further utility required to maintain that steady state is very low or say negligible. A nominal input flow variation require very low utility load.

2. Lower capital expenditure for equipments and plant machinery compare to that of conventional batch process:
Smaller capacity of equipment required in continuous process compare capacity required that in batch process.

3. Lower overhead cost :
Due to smaller the equipment and automated process certain activities like material handling ( loading & loading ) , manpower requirement and miscellaneous utensils can be lowered which reduce the overhead cost.

4. Uniform quality of intermediates and finished product in each step of process :
As the process is continuous, variation is process parameters is negligible as the efficient control systems is to be provided. While in the batch processes each batch / lot charging for reaction or operation may vary parametrically due to human error. Uniform quality of intermediates like pH of reaction mass, quantity of charged raw materials, temperature conditions while in case of finished product, uniform crystal size and shape.

5. Simplified automated process enables ease of manufacturing operations:
A PLC or DCS based automated continuous process is simpler to operate. Application of modern control systems for said continuous process like feed forward control systems for pH and temperatures , auctioneering systems for pH control in precipitator , critical relays and alarms , flow and ratio controllers can aid for effective process control in simpler way.

The process of the present invention is described by the following examples, which are illustrative only and should not be construed so as to limit the scope of the invention in any manner.

Example 1

Penicillin G –K salt (192 gm.) is dissolved in water (2400 ml) in required quantity at 25-40 deg C. Clear solution is stored in storage tank (T1).
Penicillin aqueous solution ( 8 % w/w ) is charged to enzymatic reactor (1) by using a pump (P1) at a rate of 40 ml/min from storage tank (T1). The outlet of enzymatic reactor is fed to a plug flow reactor (PFR) (2). Required temperature in range of 28-38 deg C is maintained in reactor by circulating hot water. RPM in range of 312 to 512 is maintained to keep enzymes in complete suspension. Generated PAA is continuously neutralized & pH is maintained in range of 7.8-8.2 by dosing 4 % w/w aqueous ammonia (100-120 ml) solution through pH controller.
Reaction mass is collected in storage tank (T2) and charged to jet mixer placed at top of spiral extraction column (3) via pump (P2) at a rate of 40 ml/min. Solvent dichloromethane is also charged on another end of jet mixer.,( Ratio of Aq. Mass to DCM is 1:0.25) by using a pump (P4) at a rate of 10 ml/min. Required temperature in range of 0-5 deg C is maintained in spiral column by circulating chilled water in annular space of spiral column. pH in range of 0.8 – 1.2 is maintained by pH controller to established required extraction condition by using a concentrated HCl. Extracted material trickles into spiral column and layers are gravity separated . Extracted aqueous reaction mass is collected in storage tank (T3), while extracted dichloromethane is collected in storage tank (T6).
Extracted aqueous reaction mass is charged to a continuous precipitator (4) by using a pump (P3). Required temperature in range of 0-5 deg C is maintained in precipitator by circulating chilled water in the jacket of precipitator. pH in range of 3.8 to 4.2 is maintained by pH controller to established required precipitation condition by using 20 % aqueous ammonia solution.
Precipitated crystal slurry from continuous precipitator is charged to a continuous filter screen (5), where precipitated 6-APA crystals and mother liquor is filtered under vacuum. Mother liquor is stored in storage tank (T4). 6-APA wet cake is washed with chilled methanol further to remove various color impurities.
Wet solid crystals obtained from filter is fed to vacuum dryer (6) , where vacuum conditions and temperature in range of (45-50 deg C) is maintained for 6-8 hrs till required moisture content obtain in dried crystals of 6-APA ( 100 gm).
The process can be further extended for the recovery of phenyl acetic acid (PAA) , from the rich dichloromethane (DCM) obtained in extraction stage.
In the recovery process of PAA, rich DCM and 20 % w/w aqueous ammonia solution are charged to jet mixer placed on the top of spiral extraction column (7) by using pump P5. pH in range of 8-8.5 is maintained by using pH controller . Extracted aqueous PAA rich solution is stored in storage tank (T9), and spent DCM is stored in storage tank (T8). Spent DCM can be further recycled for extraction of PAA in process step for 6-APA.
Extracted PAA aqueous mass is charged to a continuous precipitator (8) by using a pump (P6). Required temperature in range of 0-5 deg C is maintained in continuous precipitator by circulating chilled water in the jacket of precipitator. pH in range of 1.0-1.5 is maintained by pH controller to established required precipitation condition by using concentrated HCl.
Precipitated PAA crystal slurry from continuous precipitator is charged to a continuous filter screen (9), where precipitated PAA crystals and mother liquor is filtered under vacuum. Mother liquor is stored in storage tank (T10). PAA wet cake is washed with chilled water further to remove various color impurities.

HPLC purity of 6-APA~ 99.5%